Means and method for controlling high side pressure in heat transfer systems of the compression type



Jan. 20, 1959 Y D. E. KRAMER 2,869,330

MEANS AND METHOD FOR CONTROLLING HIGH SIDE PRESSURE 4 IN HEAT TRANSFER SYSTEMS OF THE COMPRESSION TYPE Filed March 8, 1955 INVENTOR BYe r $3; ATTORNEYS ilnited States Patent n MEANS AND METHOD FOR CONTROLLING HIGH SIDE PRESSURE IN HEAT TRANSFER SYSTEMS OF THE COMPRESSION TYPE Daniel Kramer, T ehton, N..I., assignor to Mercer Engineering Co., Trenton, N. J'., a co p'artnersliip Application March 8,1955, Serial No. 492,886 9 claims. (Cl. 62 -417 This invention relates' to riieans and method for controlling high side pressure in heat transfer systems of thecompression type, and has for an object to provide such a system including interconnected compressor, condenser, andevaporato'r, with a pressure reducing device in operative relationship to the evaporator inlet, and which embodies means fol-automatically maintaining the pressure in the'high side of the system, especially adjacent the said pressure reducing device, at or above a predetermined minimum regardless of ambient temperature at the condenser.

Another object is to provide for attaining the above recited pressure control without resorting to complicated or expensive construction and with the use of a single automatic valve.

Another object is to provide such a system which is admirably suited to the employment of an air cooled or evaporative condenser, and which is fully effective even though the, condenser be exposed to out doors atmospheric conditions.

Another object is top'rovide such a system which does not require any seasonal adjustment by' manipulation of hand valve or other contrivance in order to continue functionally satisfactory operation.

Another object is to provide sucha' system in Which the desired high side pressure control is achieved by adoption and unique embodiment and regulation of the siphonic principle.

Another object is to provide such a system in which pressure at the condenser outlet, and hence the level of refrigerantitherein, is regulated by a conduitin the form of 'an inverted U for theiflow of liquid refrigerant from the condenser. to a receiver, the high point of the U beingin communication'through a valve controlled bypass withthe compressor'hot gas discharge conduit Another objectis to control the flow of gas throughthe said by-pass by a constant outlet pressure valve, preferably of the modulating type, fitted therein and subject to com denser operating pressure.

Another object is to provide certain improvements in the form, construction, and arrangement of'the several parts of the system and'in thesteps of the method, where'- by the above named objects and others inherentin the invention may be effectively attained.

Inbrief suminary, the invention comprehends the provision of a refrigerating or air conditioning heat exchange system of the compression type which presents novel means and method for controlling high side pressure so as-to maintain it at or above a predetermined minimum regardless of'ambient temperature conditions, and changes therein, to which the condenser is subject. The system is of extreme simplicity structurally andin mode of operation; is entirely automatic; and requires no seasonal adjustment. The'conduitleading from condenser outlet to receiver is of inverted U or hair pin form'and, when filled with condensed refrigerant,- the down pull in the leg-of the conduit leading-to the receiver substantially or completely balances; on siphonic principle, the weight of the column Patented Jan. 20, 1959 in the other leg so that the latter exerts little, if any; pressure at the condenser outlet. The high point of the U conduit is connected through a by-pass with the hot gas compressor discharge conduit and the opening and closing of the by-pass is governed by a' valve that is. sub ject to the operating pressure of the condenser. When the latter falls below the setting of the valve due, for instance, to drop in ambient temperature at the condenser, the valve opens, hot gas enters at thehigh point ofthe U and breaks or interrupts the siphonic pull; whereupon the weight of the column of liquid in the leg of the U uprising. from the condenser outlet raises the pressure at the latter, causes rise in the level of liquid in the condenser which reduces its area of eifective heat transfer or condensing surface and thus causes risein highside pressure toat least the predetermined minimum. By using a constant outlet pressure modulating valve in the by-pa ss,,high side pressure can be maintained substantially constant above the predetermined minimum. v I I V A practical embodiment of the invention is diagrammatically represented in the accompanying drawing.

In heat exchange engineering its is known that, in a given compression type system operating under a given heat load, the high side pressure is related to the condensing temperature, which latter depends upon the relative temperature of the condensing medium or coolant. If air is the coolant, as in air cooled or evaporative con- (renters, pronounced drop in ambient temperature at the condenser can lead to a decrease in high side pressure of the system which sharply lessens" refrigerating capacity by curtailing flow through the usual thermostatic expansion valve, because of the redueed pressure differential acrossthe same and notably restricts efficient hot gas defrosting of the evaporator. A like condition may obtain when water is the condenser coolant. To illustrate, inadequacy of watersuppl'y and sewage facilities in many urba'iif areas and the impracticability of water cooling condenser's in rural areas have caused marked expansion in the use of air cooled or evaporative condensers. They are frequently located out of doors and are usually of such capacity as'to operate at a condensing temperature approximately" 15f F. above the existing ambient to insure ehiciency inwarm weather. When, however, the ambient temperature falls, the condensing temperature correspondingly falls and, in cold weather, the condensing temperature, and hence the high side pressure of the system, is apt to fall so' low that the pressure drop' acr os's the thermostatic expansion valve is insufficient to cause satisfactory supply of refrigerant to the evaporator, Again, reduction inevaporator heat load can, of itself, cause drop in high side pressure.

Having in mind the fact that the heat transfer char acteristics of evaporator and condenser differ essentially in that more complete flooding of the former increases its capacity while the opposite is true of the' latter, it will be evident that gradual flooding of the condenser with liquid refrigerant will correspondingly reduce its heat transfer capacity by lessening the area of effective heat transfer surface, and vice v'ersa. Consequently, control of the level of the'liquid refrigerant within the condenser can serve to control high side pressure and be employed to-maintain the pressure at or above a predetermined minimum. This present invention avails itself of these factors and functions automatically to maintain satisfactory high side pressure condition regardless of amhient temperature at the condenser and/or heat load in the evaporator.

Referring now to the embodiment of the invention represented in the drawing, the compressor is denoted by 1, the condenser by 2, the receiver'by 3, and the evaporator by 4. These elementsma'y' be of any known or approved form and construction, and thecondenser the outlet of the latter connects with the receiver by a conduit 8. The refrigerant supply conduit 9 interconnects the receiver and evaporator inlet and has interposed therein the usual pressure reducing device shown .as a thermostatic expansion valve 10 indicated at 11 as controlled by the customary feeler bulb. A manual service valve 12 may be fitted in the supply conduit, if

desired. Evaporator outlet and condenser intake are connected by the suction conduit 13, thus completing the circuit of the system.

As will be observed from the drawing, the conduit 8 is in the form of an inverted elongated U or hairpin, one leg of the U extending upwardly from the condenser outlet to the high point or apex of the U, indicated by 14, while the other leg extends downwardly therefrom to the receiver. A by-pass conduit connects the hot gas conduit 7 with conduit 8 at the high point 14 and in the said by-pass is fitted a regulating valve 16 of the constant outlet pressure type, preferably modulating and adjustable. Other devices functioning in a similar manner could be substituted for the valve 16, e. g. a solenoid valve controlled by pressure switch, or an automatic constant pressure expansion valve, but the constant outlet pressure valve is preferred.

The mode of operation of the system is as follows:

Valve 16 is set or adjusted to remain closed as long as the operating head or high side pressure is at or above a predetermined value, e. g. 110 lbs. per square inch. In this condition, the hot gas from the compressor flows through conduit 7 to the condenser 2, and is largely liquefied therein, passing thence through conduit 8 to the receiver 3, through supply conduit 9 to the expansion valve 10, to evaporator 4, where it performs its chilling function and turns mainly to the vapor phase, and finally back to the compressor intake for recompression and recirculation as just described. During this cycle the by-pass 15 and valve 16 are closed, and the U shape of conduit 8 is functionlessthe said conduit merely serving as a passage for the condensed refrigerant which substantially completely fills it in an unbroken stream because the siphonic down pull of the column of liquid in the leg uprising from the receiver counterbalances the down pull of the column in the other leg. This performance may be considered as continuing throughout warm seasonal weather, e. g. while the atmospheric temperature is 60 F. or higher.

Upon the advent of colder weather when the ambient temperature at the condenser falls to such a degree that the operating head or high side pressure dips below the pressure setting of valve 16, the latter will open and the functional activity of the present invention will automatically and immediately ensue, as follows:

Hot gas from conduit 7 will traverse by-pass conduit 15 and enter conduit 8 at its high point or apex 14, thereby interrupting the continuity of the liquid stream in conduit 8 and breaking the siphonic effect. This permits the column of liquid in the leg of conduit 8 that uprises from the condenser outlet to exert its weight and pressure at the said outlet and restrict the outflow from the condenser, thereby raising the level of liquid therein. This at once reduces the capacity of the condenser by lessening its area of effective heat transfer surface and elevates the operating head or high side pressure. As soon as the said pressure reaches the setting of valve 16, it will throttle and the flow of liquid through and out from the condenser will continue in the normal cycle of operation heretofore described, but at a pressure equal to the setting of valve 16. As the valve 16 is preferably modulating in character, the desired control of high side pressure is attained without abrupt or substantial variations.

The height of the inverted U or hairpin shaped conduit 8, i. e., the length of the leg which uprises from the outlet of the condenser 2 to the high point or apex 14, is related to several factors, namely, the design of the condenser; the physical height of the condenser between inlet and outlet; the B. t. u. loading of the condenser; the pressure drop across the valve 16; and the designed minimum operating head pressure at the lowest anticipated ambient temperature. The design of the condenser is significant with respect to the pressure drop across the same. The greater the drop the shorter the required height of the U. As to the physical height of the condenser, the shorter this dimension the shorter the required U. Touching the B. t. u. loading of the condenser, which involves the horsepower of the system, the greater the loading the shorter the required U. Considering the valve 16, the lower the pressure drop thereacross for the same flow therethrough, the shorter the U. In regard to operating head pressure and ambient temperature, the lower the anticipated ambient for the designed minimum operating head pressure the higher or longer the U; or, in other words, increase in designed minimum operating pressure or decrease in lowest anticipated ambient temperature leads to increase in height of the U.

To illustrate, in systems of from one half to ten horsepower, the height of the U may vary from four to six and one half feet; and the six foot height is suitable for a condenser with a height of as much as four or five feet from outlet to inlet, a designed operating head pressure of lbs. per square inch and an ambient of zero degrees F., when using Freon 12 as refrigerant, with a constant outlet pressure valve set at the desired pressure. With this example and the above listed pertinent factors in mind, the engineer in this industry will have no ditliculty in determining, by calculation or empirically, the most desirable height for the U in any given system.

Referring to the relative lengths of the two legs of the U conduit 8, it is desirable that the leg which uprises from the receiver be at least as long as the leg which uprises from the condenser outlet. The former may be longer than the latter, as shown in the drawing, without functional advantage or disadvantage. It may here be observed that the pressure at the high point 14 is always less than at the condenser outlet, whether valve 16 be open or closed. When the valve is closed, the siphonic pull in the leg that uprises from the receiver offsets the pressure weight of the other leg at the condenser outlet, but the opening of the valve interrupts this pull and permits the hereinabove described rise in pressure at the condenser outlet with its effect upon the liquid level therein.

When, in the specification and claims reference is made to counterbalancing the weight of the liquid in the leg of conduit 8 that arises from the condenser outlet, precise counterbalancing is not a required meaning as a functionally operative condition is suflicient. Likewise, and for the same reason, the legs of the inverted U need not be in precise parallelism.

It should be noted and emphasized that the present invention afiords a system and mode of operation or method of control which is entirely automatic and requires but one valve aside from the usual thermostatic expansion valve at the evaporator. There is no requirement for a manual valve to be opened or closed according to seasonal changes, nor for a solenoid valve governed by thermostat or pressurestat for the same purpose, or for other equivalent device, or for a critically sized restrictor tube or the like. Thus, simplicity with important economy is attained along with full automaticity regardless of seasonal ambient temperature, which is believed to be a marked improvement over previous systems designed for the control of head or high side pressure.

It will be understood that various changes may be resorted to in the form, construction, and arrangement of the several parts of the system and steps of the method of control without departing from the spirit or scope of the invention; and, hence, I do not intend to be limited to details herein shown or described except as the same may be included in the claims or be required by disclosures of the prior art.

What I claim is:

1. In a compression type heat exchange system having a conduit interconnected circuit including compressor, condenser, high pressure receiver for receiving condensed refrigerant from the condenser, and evaporator, automatically operating means for preventing the fall of high side pressure below a predetermined minimum by controlling the effective area of heat transfer surface within the condenser, said means comprising, a hot gas conduit connecting the compressor discharge with the condenser inlet, a conduit leading from the condenser outlet to the said receiver which up-rises from the condenser outlet to a height above the condenser, a by-pass conduit connecting the hot gas conduit to a point higher than the condenser in said conduit that leads from condenser outlet to receiver, and means for controlling flow through said by-pass, the parts being so constructed and arranged that, when the conduit connecting condenser and receiver is filled with refrigerant and flow is permitted through the by-pass, the liquid column in the conduit up-rising from the condenser outlet will exert pressure at the said outlet,

and restrict out-flow therefrom.

2. A system as defined in claim 1, in which the means for controlling flow through the by-pass is operatively subject to the high side pressure of the system.

3. In a compression type heat exchange system having a conduit interconnected circuit including compressor, condenser, high pressure receiver and evaporator, automatically operating means for preventing the fall of high side pressure below a predetermined minimum by controlling the effective area of heat transfer surface within the condenser, said means comprising, a hot gas conduit connecting the compressor discharge with the condenser inlet, a conduit leading from the condenser outlet to the receiver, said last named conduit embodying two legs joined at their tops, one leg up-rising from the condenser outlet to a height above the condenser and the other leg extending downwardly from their top joining point, the parts being so constructed and arranged that, when the said last named conduit is filled with liquid, the liquid column in the last named leg will exert a. siphonic pull on the liquid column in the first named leg, 9. by-pass conduit connecting the hot gas conduit to a point higher than the condenser in the conduit that leads from the condenser outlet to the receiver, and a fiow regulating device operatively subject to the high side pressure positioned in the by-pass conduit.

4. A system as defined in claim 3, in which the flow regulating device is a constant outlet pressure valve.

5. A system as defined in claim 4, in which the constant outlet pressure valve is of the modulating type.

6. A system as defined in claim 3, in which the point of connection of the by-pass conduit with the conduit that leads from the condenser outlet to the receiver is the high point of the last named conduit, the parts being so constructed and arranged that flow of gas through the by-pass will interrupt the siphonic pull and permit the liquid column in the leg of the last named conduit which up-rises from the condenser outlet to exert pressure at the latter and restrict outflow therefrom.

7. A method of preventing the fall below a predetermined minimum of high side pressure in a compression type heat exchange system having a circuit including compressor, condenser, receiver and evaporator, which method comprises the steps of providing an uprising column of liquid at the condenser outlet, restraining the downward pressure of the column when the high side pressure of the system is above the predetermined minimum, and interrupting said restraint upon drop of the high side pressure to the said minimum.

8. A method as defined in claim 7, in which restraining the downward pressure of the column is accomplished by siphonic pull upon the column.

9. A method as defined in claim 7, in which interrupting the restraint is accomplished by the injection of gas into the column.

References Cited in the file of this patent UNITED STATES PATENTS 1,880,653 Boars Oct. 4, 1932 2,081,883 Philipp May 23, 1937 2,443,500 Goddard June 15, 1948 2,710,507 Ashley June 14, 1955 

